Vertebrate photoreceptor cell outer segment structure and light-induced structure changes will be studied using birefringence, light-scattering, absorption, dichroism and histochemical techniques. The molecular-level basis for the axial differences in rod disk membrane structure and composition will be investigated. An analysis of membrane structure in outer segments from animals with dystrophic and degenerating retinas will be made to see if submicroscopic structural changes precede gross morphological damage. Light-induced structural changes monitored by birefringence and light-scattering measurements will be further characterized. Their possible roles in visual transduction, adaptation and regeneration will be assessed.